Newbie Lens/Focal Length Question

"Capt Donkey Smile" wrote in message
oups.com...
Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

Well, with a zoom lens you can change the focal length, yes. That's what
zoom lens means. Changing the focal length changes the image size in
direction proportion, e.g. 2x the focal length = 2x the image size.



I understand that 50mm sees things pretty much as I see it.

Actually, NO camera lens really "sees thing pretty much as [you] see it,"
for a lot of reasons. Your visual angle of view (assuming normal eyesight)
is much wider than the field of view of a 50mm lens, as you can easily see
for yourself. On the other hand, most of what you can see over that wide
field of view (typically about 180 degrees horizontally) you cannot see very
sharply, while the 50mm lens covers everything sharply. Also, your eye's
"film," the retina, is essentially the inside of a hemisphere whereas in a
film or digital camera the corresponding sensor is flat. So there is just no
way any conventional camera can really see as your eye sees.

The 50mm lens (on a 35mm camera) has been regarded as "normal" for decades.
That doesn't mean the camera with such a lens sees as your eye sees, only
that it produces an image that "looks about right," neither too wide nor too
narrow in angle of view. Actually the 50mm lens is a little long for
"normal" on a 35, since traditionally "normal" has meant equivalent to the
diagonal of the negative--which would be about 43mm on a 35. "Normal" lenses
for 35s have been made with all sorts of focal lengths, from 40 to 58mm at
least. There is nothing sacred or cosmically significant about 50mm.



I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

Right, a 30mm lens on such a camera would give you the equivalent of 50mm on
a 35. Just don't take that focal length as being too important, as it is
not.



If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Depends. Most zoom lenses are somewhat wide angle at the short end, not
"normal." If you assume that you want a zoom that STARTS at around "normal"
then yes, something equivalent to 50-500mm would be the 10x zoom you'd look
for. But much more usual is a 10x zoom somewhat wider at the short end, like
38-380mm.



Thanks

N.

"Charles Schuler" wrote in message
...


I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

Prime lenses are fixed in FL and zoom lenses allow a range of FLs.

No offense, but there are already so many well-meaning people ignorantly
misusing "prime lens" in this way, it sure would be nice if we could stop
encouraging innocent newbies to parrot the same mistake.

A prime lens is THE CAMERA LENS, as opposed to some other optical device
used with it. A zoom lens is a prime lens just as much as a fixed focal
length (FFL) lens is.

"Prime" is correctly used here in the sense of primary, chief or original.
There is NO definition for "prime" that means fixed focal length or fixed
anything else.

N.

"Charles Schuler" wrote in message
...


I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

Prime lenses are fixed in FL and zoom lenses allow a range of FLs.

No offense, but there are already so many well-meaning people ignorantly
misusing "prime lens" in this way, it sure would be nice if we could stop
encouraging innocent newbies to parrot the same mistake.

A prime lens is THE CAMERA LENS, as opposed to some other optical device
used with it. A zoom lens is a prime lens just as much as a fixed focal
length (FFL) lens is.

"Prime" is correctly used here in the sense of primary, chief or original.
There is NO definition for "prime" that means fixed focal length or fixed
anything else.

N.

"Nostrobino" wrote in message
m...

"Charles Schuler" wrote in message
...


I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

Prime lenses are fixed in FL and zoom lenses allow a range of FLs.

No offense, but there are already so many well-meaning people ignorantly
misusing "prime lens" in this way, it sure would be nice if we could stop
encouraging innocent newbies to parrot the same mistake.







Prime lens.

A lens with a fixed focal length - its field of view cannot be changed. At
least, not without the addition of supplemental lenses or teleconverters.

Generally, prime lenses are lighter, sharper, cheaper and of higher
optical quality than zoom lenses, since it's easier to build a prime lens
than a zoom. By tradition, common prime lenses used by 35mm cameras are
lenses with 28, 50, 85, 100 and 135mm focal lengths.

Nostrobino wrote:

No offense, but there are already so many well-meaning people
ignorantly
misusing "prime lens" in this way, it sure would be nice if we could
stop
encouraging innocent newbies to parrot the same mistake.

No offence, but if you could start spelling "offence" properly -- as it
was originally spelled in English -- and not encouraging linguistic
neophytes from propagating the same mistake, maybe your argument would
have slightly more than the zero force it presently has?

A prime lens is THE CAMERA LENS, as opposed to some other optical
device
used with it. A zoom lens is a prime lens just as much as a fixed
focal
length (FFL) lens is.

"Prime" is correctly used here in the sense of primary, chief or
original.
There is NO definition for "prime" that means fixed focal length or
fixed
anything else.

Tilt on, man! Tilt on!

No offense, but there are already so many well-meaning people ignorantly
misusing "prime lens" in this way, it sure would be nice if we could stop
encouraging innocent newbies to parrot the same mistake.

No offense taken, but you have stated one point of view.
From the dictionary at PhotoNotes.Org:


"Prime lens.

A lens with a fixed focal length - its field of view cannot be changed. At
least, not without the addition of supplemental lenses or teleconverters.

Generally, prime lenses are lighter, sharper, cheaper and of higher
optical quality than zoom lenses, since it's easier to build a prime lens
than a zoom. By tradition, common prime lenses used by 35mm cameras are
lenses with 28, 50, 85, 100 and 135mm focal lengths."



Check other sources ... the definition of a prime lens, as presented, is
widely used.



Cheers

No offense, but there are already so many well-meaning people ignorantly
misusing "prime lens" in this way, it sure would be nice if we could stop
encouraging innocent newbies to parrot the same mistake.

No offense taken, but you have stated one point of view.
From the dictionary at PhotoNotes.Org:


"Prime lens.

A lens with a fixed focal length - its field of view cannot be changed. At
least, not without the addition of supplemental lenses or teleconverters.

Generally, prime lenses are lighter, sharper, cheaper and of higher
optical quality than zoom lenses, since it's easier to build a prime lens
than a zoom. By tradition, common prime lenses used by 35mm cameras are
lenses with 28, 50, 85, 100 and 135mm focal lengths."



Check other sources ... the definition of a prime lens, as presented, is
widely used.



Cheers

"Capt Donkey Smile" wrote in
oups.com:

Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

no. "sees things as i see it" depends more than on just the focal length.
also, using digital instead of film doesn't change focal lengths.
nor would it adjust the scale of things as you view them through the
viewfinder.

--
http://www.neopets.com/refer.phtml?username=moosespet

"Randy L." wrote in
:

Capt,
My understanding is that the 50mm = 1x rule is correct for 35mm
film
cameras, but that for digital SLR's it more like a focal length of
35mm = 1x due to the smaller size of the CCD.

That's not correct. the size of your capture area doesn't change how much
magnification is produced by your lense, nor does it change what you see
through the viewfinder. If you had a ccd that was the identical size of a
35mm negative, and then replaced it with one that was only 1/4 the size,
you wouldn't then need a different lense to get the same image proportions.


--
http://www.neopets.com/refer.phtml?username=moosespet

wrote in message
oups.com...
Nostrobino wrote:

No offense, but there are already so many well-meaning people
ignorantly
misusing "prime lens" in this way, it sure would be nice if we could
stop
encouraging innocent newbies to parrot the same mistake.

No offence, but if you could start spelling "offence" properly -- as it
was originally spelled in English --

Many words are spelled differently in American English than in British
English, and this is one of them. Many are pronounced differently too; for
example we say and write "aluminum" where they use "aluminium." We also say
"fenders" where the Brits say "wings," they call "petrol" what we call
"gasoline," and so on.

It is not the SPELLING of "prime" I'm objecting to, but its misusage. Spell
it "pryme" if you like. Just don't use it for "fixed focal length," please.

N.